Which of the following statements about diamond is true?
A. It has a layered structure
B. It is the hardest natural substance
C. It is a good lubricant
D. It conducts electricity
Answer: Option B
Solution (By JKExamLibrary)
Diamond has a rigid 3D covalent network, making it the hardest natural material. It does not conduct electricity (no free electrons). It is not layered (graphite is). It is used as an abrasive, not a lubricant.
Explanation:
This is a single displacement reaction. Iron (Fe) is more reactive than Copper (Cu), so it displaces copper from its aqueous sulfate solution. The blue color of CuSO₄ fades, and a brown deposit of Cu forms. Reactivity series dictates that a more reactive metal displaces a less reactive one.
Explanation:
Temporary hardness is due to dissolved bicarbonates of Ca and Mg, which can be removed by boiling: Ca(HCO₃)₂ → CaCO₃↓ + H₂O + CO₂. Permanent hardness is caused by chlorides and sulfates of Ca and Mg, not removed by boiling. Sodium bicarbonate does not cause hardness. Methods to remove permanent hardness include treatment with washing soda (Na₂CO₃), ion exchange, or calgon.
Explanation:
Cement sets by hydration reactions forming C-S-H gel and Ca(OH)₂, even underwater. It's a chemical process, not drying. Gypsum controls the setting rate.
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